Somatic cells can be reprogrammed into induced pluripotent stem cells (iPSCs) by the enforced expression of transcription factor combinations such as Oct4, Klf4, Sox2 and c-Myc (OKSM) (Takahashi and Yamanaka, 2006), generating a unique platform to study developmental processes and model disease in cell culture (Cherry and Daley, 2013). An intriguing hallmark of induced pluripotency is the comparatively low efficiency at which stable pluripotent cell lines are established, which ranges between 0.1 and 10% for most somatic cell types (Stadtfeld and Hochedlinger, 2010). This is associated with the asynchronous reactivation of endogenous pluripotency loci such as Oct4, Nanog and Utf1 and a lag phase of two or more weeks before a self-sufficient pluripotent state is established, which is only successful in a small subset of cells (Buganim et al., 2012; Polo et al., 2012). Studies in fibroblasts, the most commonly used cells for iPSC derivation, suggest that the gradual establishment of a chromatin environment permissive for OKSM activity may underlie these slow and stochastic reprogramming kinetics (Apostolou and Hochedlinger, 2013; Koche et al., 2011; Soufi et al., 2012). Intriguingly, some somatic cell types appear more amenable for the extensive epigenetic remodeling associated with acquisition of pluripotency. For example, within the hematopoietic system, immature progenitors form iPSCs more readily than differentiated cells (Eminli et al., 2009). The molecular reasons for this observation, however, remain unknown.
In agreement with the importance of chromatin remodeling for iPSC formation, small molecule compounds that alter the activity of chromatin-modifying enzymes can facilitate fibroblast reprogramming (Li et al., 2013). An example is the antioxidant ascorbic acid (AA), which serves as co-factor for α-ketoglutarate-dependent dioxygenases such as Tet proteins and Jmj C-domain-containing histone demethylases (Monfort and Wutz, 2013). Enhancement of iPSC formation has also been reported upon modulation of cellular signaling pathways. For example, activation of Wnt signaling by natural ligands (Marson et al., 2008) or chemical inhibition of GSK3 (Li and Ding, 2010), an antagonist of β-catenin, has been shown to promote iPSC formation. However, evidence for an inhibitory role of the Wnt pathway early in reprogramming has also been provided (Aulicino et al., 2014; Ho et al., 2013). Inhibition of TGFβ signaling supports both early (Li et al., 2010; Samavarchi-Tehrani et al., 2010) and late events (Ichida et al., 2009; Maherali and Hochedlinger, 2009) during the transition of fibroblasts to a pluripotent state.
Several publications and patent documents are referenced in this application in order to more fully describe the state of the art to which this invention pertains. The disclosure of each of these publications and documents is incorporated by reference herein.